Hardened VoIP System

ABSTRACT

A hardened VoIP system is presented that includes secure push-to-talk voice functionality. Through the addition of encryption, authentication, user filtering, and integration with new and existing LMR systems, a secure voice platform ensures malicious software, unauthorized access and brute force security attacks will not compromise the voice communications of the system. The VoIP system is engineered to ensure graceful system degradation in the event of maintenance activities, natural disasters and failure modes. The hardened VoIP system offers the functions a LMR trunking system while utilizing broadband connections. Private calls, group calls, Emergency Alarms with covert monitoring capability, scanning and priority scanning may be incorporated into the system. The system includes a VoIP controller that serves as a trunking controller, manages available VoIP based conference bridges, and assigns them as needed to the parties involved in each voice call.

CROSS REFERENCE TO CO-PENDING APPLICATION

This application is a continuation of U.S. patent application Ser. No.16/055,432 titled “Hardened VoIP System” filed on Aug. 6, 2018, issuedas U.S. Pat. No. 10,298,384 on May 21, 2019, and was a continuation ofapplication Ser. No. 15/584,688 that was filed on May 2, 2017 and issuedas U.S. Pat. No. 10,044,498 on Aug. 6, 2018 and claimed priority to U.S.Provisional Patent Application 62/435,562 filed Dec. 16, 2016 andentitled “Hardened VoIP System,” the contents of which are herein allfully incorporated by reference.

FIELD OF THE INVENTION

The present invention relates generally to fault tolerant mobilecommunication systems, and specifically relates to hardened voice overIP (VoIP) systems with push to talk (PTT) functionality that integrateinto existing land mobile radio (LMR) systems.

BACKGROUND OF THE INVENTION

LMR systems are wireless communications systems generally intended foruse by terrestrial users in vehicles or on foot. Such systems are oftenused by emergency first responder organizations such as police, fire andambulance services, public works organizations, dispatched services suchas taxis, and companies with large vehicle fleets or numerous fieldstaff. LMR systems are often independent, but can be connected to otherfixed systems such as the public switched telephone network (PSTN) orcellular networks.

Radio over Internet Protocol (RoIP) is similar to VoIP, but augmentstwo-way radio communications rather than telephone calls. With RoIP, atleast one node of a network is a radio (or a radio with an IP interfacedevice) connected via IP to other nodes in the radio network. The othernodes can be two-way radios, but can also be dispatch consoles, eithertraditional (hardware) or modern (software on a PC), plain old telephoneservice (POTS) telephones, softphone applications running on a computersuch a smartphone or some other communications device accessible overIP. RoIP has been deployed over private networks as well as theInternet. RoIP has shown to be useful in land mobile radio systems usedby public safety departments and utility fleets spread over a broadgeographic area. Like other centralized radio systems such as trunkedradio systems, issues of delay or latency and reliance on centralizedinfrastructure can be impediments to adoption by public safety agencies.

Examples of previous attempts to integrate LMR with VoIP include U.S.Pat. No. 8,145,262 issued to Martinez that claims to disclose amultimode LMR and a method of communicating LMR content using an LMRdevice. The Martinez LMR system includes an LMR communication portionand a cellular data network communication portion.

U.S. Pat. No. 8,169,983 issued to Janky claims to disclose a transcoderarchitecture and method for transcoding in LMR systems. The Janky LMRsystem includes a first communication site configured to communicateusing a first LMR communication protocol and a second communication siteconfigured to communicate using a second LMR communication protocol. TheJanky LMR system further includes a transcoder configured to receive LMRcontent from the first communication site communicated using the firstLMR communication protocol and digitally convert the LMR content to thesecond LMR communication protocol to be communicated to the secondcommunication site.

U.S. Pat. No. 8,634,799 issued to Economy claims to disclose an incidentcommander computing device that dynamically reconfigures subscriber unitusage of radio access networks by first identifying, based at least on atype of incident occurring within a particular geographic area, a firstincident response group having a first higher priority for responding tothe incident and a second incident response group having a second lowerpriority for responding to the incident, then identifying a first higherpriority radio access network having a sufficient coverage level acrossthe particular geographic area and a second lower priority radio accessnetwork having a sufficient coverage level across the particulargeographic area, and finally assigning the first incident response groupto the first higher priority radio access network and assigning thesecond incident response group to the second lower priority radio accessnetwork.

U.S. Pat. No. 8,676,243 issued to Blanco claims to disclose acommunication system that provides dual-watch and multi-watch capabilityfor group PTT services where incoming PTT calls are prioritized andplayed out in accordance with prioritization protocols. In the Blancosystem a user of multiple communication devices can hear received audiotraffic being played out in accordance with the priority assigned to thegroup call and the priority assigned to the communication device, andnumerous calls can be simultaneously received and managed.

SUMMARY OF THE INVENTION

A hardened VoIP system is presented that includes secure PTT voicefunctionality. Through the addition of encryption, authentication, userfiltering, and integration with new and existing LMR systems, a securevoice platform ensures malicious software, unauthorized access and bruteforce security attacks will not compromise the voice communications ofthe system. The VoIP system is engineered to ensure graceful systemdegradation in the event of maintenance activities, natural disastersand failure modes. The hardened VoIP system offers the functions a LMRtrunking system while utilizing broadband connections. Private calls,group calls, Emergency Alarms with covert monitoring capability,scanning and priority scanning may be incorporated into the system. Thesystem includes a VoIP controller that serves as a trunking controller,manages available VoIP based conference bridges, and assigns them asneeded to the parties involved in each voice call.

The system allows for standard LMR functionality and the ability forsupervisor tablets and smartphones to participate in and monitor VoIPcalls between the dispatch center, mobile workforce and revenuevehicles. The system also provides supervisor tablets and smart phonesthe capability to scan talk groups in active calls, setup calls to otherusers, including closed microphone users, without dispatch or otherthird party intervention using the private call feature.

The hardened VoIP system provides an integrated mobile product thatallows the system to gracefully fallback to the LMR infrastructure inthe event of a broadband network outage. The integration of hardenedVoIP and LMR allows new or existing LMR capital resources to be used tobridge various radio technologies and further allows switchingalgorithms to seamlessly and gracefully degrade from hardened VoIP toLMR without user intervention in the event of a broadband outage.

BRIEF DESCRIPTION OF THE DRAWINGS

Preferred embodiments are described with reference to the followingdrawings, wherein:

FIG. 1 illustrates an exemplary embodiment of a hardened VoIP system.

FIG. 2 illustrates an example of a VoIP solution for mobile devices.

FIG. 3 illustrates an improved VoIP solution for mobile devices.

FIG. 4 illustrates a method of a VoIP controller registering clientdevices and updating talk group databases.

FIG. 5 illustrates an example of data that may be found in a talk groupdatabase.

FIG. 6 is a flow diagram of a client device transitioning betweennumerous communication methods and systems.

DETAILED DESCRIPTION

The present invention may be used with any type of hardenedcommunication system and is particularly suited for police, fire, andtransit systems. However, for descriptive purposes, the presentinvention will be described in use with a municipal bus system.

FIG. 1 shows a schematic of a hardened VoIP communication system 10 thatincludes a server 105 connected to a switch 110 that relays data to adata communication controller 115. Users may configure and/or monitorthe system through the use of client devices 120 with access the switch110. The server 105 also communicates with the VoIP channel controller125 that receives and stores data from a VoIP database 130. The channelcontroller 125 is configurable to transmit data to both a local VoIPswitch 135, a hosted VoIP Switch 140, and a hosted conference bridge145. The local VoIP switch 135, the hosted VoIP switch 140, and thehosted conference bridge 145 are all session devices 137 that create SIPRTP sessions with mobile devices. A terminal 150 may be used to accessand/or configure the VoIP Channel controller 125.

The VoIP switches (135, 140) are configured to communicate withcommercial cellular towers 155 to transmit communications in an LTE,WiMax, EvDO UMTS, HSPA or similar format to distant communicationdevices.

In addition to communicating with the cellular towers 155 via the VoIPcannel controller 125, the server 105 is configured to also be able tocommunicate with the cellular towers 155 via the switch 110 through afirewall 160. In one example of the system, the switch 110 transmitsdata to the cellular towers 155 via an access point name gateway whilein alternative embodiments an independent internet service provider isutilized to transmit data to the cellular towers.

In addition to communicating through cellular data formats, the switch110 may transmit communications data through a firewall 165 to a server170, such as a Zetron ACOM EVO server, that relays the communication toa dispatch switch 175 and a router panel 180 such as the Telex IP-224Dual IP Remote Adapter Panel. The router panel 180 is connected by 4wire audio to an RoIP rack 185 with Ethernet or cellular dataconnectivity and also via 4 wire audio to auxiliary LMR radios 190.Dispatchers may access the system through a console client 195 such as aZetron ACOM EVO Client that communicates with the dispatch switch 175via a dispatcher server 200.

A DMZ switch 205 is connected to the dispatch switch 175 and acts as ademilitarized zone, or perimeter network, that contains and exposes thesystem's external-facing services to a larger untrusted network. Inaddition to the DMZ switch 205, the radio dispatch functionality is alsoprotected by another firewall 210.

The land mobile radio equipment includes LMR towers 215 that communicatewith first and second routers (220, 225) via a backhaul switch 230. Thefirst router 220 communicates with a LAN switch 235 and receivescommunications from VMS servers (240, 245). The second router 225communicates with the DMZ switch 205, a gateway GPRS Support Node 250and a PDG 255 via a second LAN switch 260.

By transmitting via both the cellular towers 155 and the LMR towers 215,the system is able to communicate with a variety of devices includingLMR based devices 265 such as the Motorola APX6500. The system is ableto communicate with bi-functional devices 270 such as the Motorola LEXL10 that has LTE connectivity as well as LMR connectivity. Additionally,the bi-functional devices 270 may be used to extend connectivity toWi-Fi devices 275 that are closely located with the bi-functionaldevices 270. The system may also communicate with cellular exclusivedevices 280 such as the Digi Router WR44, a commercial grade cellular toWi-Fi converter. Through a Universal Radio Logic Controller 285 andproprietary onboard hardware 290, the cellular exclusive device 280provides data to a vehicle logic unit 295 that delivers processing powerand communication with other on-board technologies and may providereal-time access to schedule, route and traffic information, on-timeperformance data, and messages to and from dispatch. The Universal RadioLogic Controller 285 and the vehicle logic unit 295 are also beconnected to an LMR Radio 300 that provides redundancy in the event offa malfunction in the cellular towers 155 or the cellular exclusivedevice 280.

The VoIP channel controller 125 of the illustrated system is a hardenedVoIP controller and is configured to provide VoIP encryption,authentication, authorization, and accounting in a bandwidth efficientmanner for the system. The VoIP channel controller 125 is shown as asingle device in FIG. 1, however it should be appreciated that multiplegeographically redundant VoIP channel controllers may be utilized inexemplary embodiments of the system such that an occurrence (fire,flood, power outage, etc.) at a single location would not disruptcommunications in the overall system.

The RoIP rack 185 performs 4 wire LMR to VoIP conversions and hasEthernet or cellular connectivity. While there is a single RoIP rack 185shown in FIG. 1, in an exemplary embodiment there is one module per talkgroup such that multiple RoIP racks may be utilized by the system. Inthe event of an RoIP rack failure, the multi-rack system is configuredto automatically shift talk groups over to any available module on theother RoIP racks to ensure seamless degradation of the system upon acomponent failure.

The console client 195 is interfaced with the RoIP rack 185 and allowsdispatchers to access specific talk groups, and or reconfigure specifictalk groups as needed. CSSI, DFSI, and AFSI links may also be used tointerface to LMR radio infrastructure.

FIG. 2 illustrates an example of a call setup from a client device 120to a vehicle with a vehicle logic unit 295. The client 120 sends a setupmessage 305 to the server 105 that responds with a call progress message310 that includes conference and channel numbers. Using the receivedinformation, the client device 120 establishes a conference bridge 315to the session device 137 and transmits a call status confirmation 320to the server 105 that relays a control message 325 to the vehicle logicunit 295 that in turn establishes a conference 330 with the preselectedsession device 137 while transmitting a confirmation 335 to the server105. The server 105 then provides a progress message 340 to the clientdevice 120.

While the system of FIG. 2 provides mobile VoIP capabilities there are afew issues with the system. In particular, the system requires a largeamount of system bandwidth (e.g., 12 Mbps for a 350 vehicle call) due toiLBC vocoder requirements. Additionally, the system loses operability ifthe server 105 is taken offline or if the system is placed in toadministrative fall back.

FIG. 3 illustrates an improved example of a VoIP call setup from aclient device 120 client to a vehicle with a vehicle logic unit 295. Inthe illustrated example, the client device 120 sends a setup message 345to the server 105 which relays the setup request 350 to the datacommunications controller 115. The data communications controller 115transmits a setup signal 355 to the cellular exclusive devices 280 suchas the Digi Router WR44 on board a vehicle. The cellular exclusivedevice 280 relays the setup request 360 to the vehicle logic unit 295via the universal radio logic controller 285. In response to the setuprequest, the vehicle logic unit 295 sends a configuration communication365 to the universal radio logic controller 285 to unmute audio andenable push-to-talk communication. The vehicle logic unit 295 sends anacknowledgment 370 to the data communications controller 115 wherein thevoice call setup is relayed 375 to the client device 120 via the server105. The client device 120 selects 380 the voice resource for theconsole client 195. The server 120 relays (385, 390, and 395) a VoIPcall setup request to the Universal Radio Logic Controller 285 and aVoIP module 286 with Universal Radio Logic Controller 285. The VoIPmodule 286 establishes at 400 a session initiation protocol (SIP)real-time protocol (RTP) session with one of the session devices 137(local VoIP switch 135, the hosted VoIP switch 140, or the hostedconference bridge 145). Upon the completion 405 of the session (eitherintentionally or unintentionally) the Universal Radio Logic Controller285 signals 410 the vehicle logic unit 295 which relays (415, 420) thetermination of the session to the client device 120 via the datacommunication controller 115.

FIG. 3 illustrates an example of a registration method and gracefulfallback in the event of a system deterioration. In step 425, the VoIPcontroller receives an initiation communication from a user clientdevice and assigns the device to a talk group (fire talk group, transittalk group, police talk group, etc.). At regular intervals, at step 430,the VoIP controller transmits control signals to the client devices. Theregular flow of transmissions from the VoIP controller to the clientdevices allows the Universal Mobile Access Radio Link Control (URLC)devices on the client devices to quickly determine if there has been adeterioration in the cellular based communication. In addition toregularly transmitting control signals in step 430, the VoIP controlleris configured to regularly receive status updates from client devices atstep 435. Similar to the control signal from the VoIP controllerallowing the client devices to determine if there has been a breakdownin VoIP communications, the status signals from the client devices allowthe VoIP controller to determine which devices are active. In anexemplary embodiment of the invention, the control signals and statussignals are both of small file size such that the cellular data usage isminimized while the system is in standby mode.

At step 440, the VoIP controller updates the database associated withactive client database. Shown in FIG. 5 are examples of some of theinformation that may be associated with the various clients in theactive client database. In step 445, the VoIP controller receives anintentional shutdown signal from a first client device, and in step 450the VoIP controller removes the first client device from the activeclient database.

In step 455, the VoIP controller fails to receive a regular statussignal from a second client device. Reasons for possible loss in signalinclude the second client device moving outside of a zone havingcellular data coverage, a problem with a cellular tower, or amalfunction with the cellular data transmitter associated with thesecond client device. Before the cellular data communication failure,LMR communication frequencies were associated with the second clientdevice and stored by both the second client device and the VoIPcontroller. With the cellular breakdown, the predetermined LMRfrequencies are assigned to the second client device, and at step 460the talk groups unassociated with the second client device arereassigned LMR communication frequencies. At step 465, in response to apush-to-talk signal, the VoIP controller facilitates a voicecommunication to the client devices in the first talk group. While thesecond client device receives communications via LMR, the other devicesin the talk group may receive the communication via cellular data, oreven local Wi-Fi. In an exemplary embodiment of the invention, thetransition from cellular LTE to LMR communications occurs seamlessly andwithout any manual configuration by the users of the client devices. Inone embodiment of the invention, the system initiates the transitionfrom LTE to LMR communications upon a detection that the LTE signalstrength has fallen below a non-zero predetermined threshold.

FIG. 5 illustrates some of the information that is stored by the VoIPcontroller in the active client database. With each client device theremay be stored a unique device identifier 470 along with a MAC address475 associated with Wi-Fi communications and an IMEI 480 associated withcellular communications. The talk group 485 associated with each groupis stored in the active client database along with the currentlyutilized communication form 490 and the talk 495 and receive 500frequencies for backup LMR communications. Client devices 501-505 arelisted as being in the first talk group while client devices 506-509 arein the second talk group. Most of the client devices (501, 502, 505,506, 508, and 509) are utilizing cellular communications protocols whiletwo devices (503, 504) are communicating via LMR and one device 507 iscommunicating via a Wi-Fi link. The forms of communication in thedatabase are not static and are expected to change. As an example, aclient device 507 may be associated with a fire truck parked at afirehouse that communicates with the VoIP controller via the firehouseWi-Fi. When the firetruck leaves the firehouse, the client device 507automatically switches over to a cellular communication protocol oncethe firehouse's Wi-Fi access point is out of range. Should cellular andWi-Fi communications be unavailable, the client device 507 on thefiretruck would automatically begin to communicate using thepredetermined land mobile radio frequencies (857.3375 and 860.3375 MHz).In an exemplary embodiment of the invention, the transition from Wi-Fito cellular data to LMR and back is done automatically without anyclient user interaction and provides seamless fallback functionalitysuch that a user may communicate using numerous different methods(Wi-Fi, LMR, satellite, etc.) without the user being aware that a changehas occurred.

FIG. 6 illustrates an example of a client device gracefullytransitioning between multiple communication methods. At step 510, theclient device regularly receives a control signal from a VoIP controllervia Wi-Fi while the client device is in standby mode. A SIP/RTP bridgecould be established by the VoIP controller upon a request to talk by auser. At step 515, the URLC aboard the client device detects that thecontrol signal has not been received and transitions the client deviceto cellular communications. At step 520, the client device is once againin standby mode and at step 525 a SIP/RTP bridge is created between theclient device and the VoIP controller in response to a voicecommunication. At step 530, the SIP/RTP bridge is terminated, and atstep 535 the client device fails to receive the control signal viacellular or Wi-Fi communications so the client device transitions toland mobile radio communications. At step 540, the VoIP controllerreceives a LMR communication from the client device, and via cellularcommunications, establishes a SIP/RTP bridge with the other members ofthe client device's talk group. At step 545, the client device receivesthe control signal via Wi-Fi, and the LMR transmitter on the clientdevice is deactivated.

In addition to the features previously discussed, numerous otherfeatures may be incorporated into the hardened VoIP system. For example,an authentication subsystem may be used to validate that a device isallowed to access the hardened VoIP infrastructure, and an authorizationsubsystem may be used to ensure that a user and a user's password forthe system are valid. Numerous accounting/billing schemes may beutilized by a variety of agencies or groups. For example, a taxidispatch system may purchase a hardened VoIP system while offsetting aportion of the cost by selling talk group functionality to otherorganizations or even individuals.

Numerous agencies (fire, police, EMT, etc.) of a municipality may besupported by a single system, and the talk group trunking functionalitymay be utilized to allow the various agencies to share communicationslines without interfering with each other. The system may includeencryption functionality that provides various levels of encryption toensure user compliance with privacy, local, state and federalregulations. A Network Management Subsystem client may also be used thatallows for the addition, deletion, and editing of system parameters suchas system IDs, talk groups, agencies, usernames, device IDs andpasswords. The system may be configured to allow two users to converseor text without the rest of the user group hearing the conversation, aprivate call feature may be implemented to allow communications betweentwo users rather than being broadcast to the active registered talkgroup users.

The inventors contemplate several alterations and improvements to thedisclosed invention. Other alterations, variations, and combinations arepossible that fall within the scope of the present invention. Althoughvarious embodiments of the present invention have been described, thoseskilled in the art will recognize more modifications that may be madethat would nonetheless fall within the scope of the present invention.Therefore, the present invention should not be limited to the specificexamples described.

1. A system for providing hardened VoIP and land mobile radiocommunication services to mobile devices, the system comprising: acontroller configured in a first standby state to receive via a cellularcommunications system a first heartbeat signal from a first mobiledevice and a second heartbeat signal from a second mobile device,transmit via the cellular communications system a first status controlsignal to the first mobile device and a second status control signal tothe second mobile device, and maintain a database with a firstidentifier associating the first mobile device with the cellularcommunications system and a second identifier associating the secondmobile device with the cellular communications system; in a secondstandby state to receive via the cellular communications system thesecond heartbeat signal from the second mobile device, transmit via thecellular communications system the second status control signal to thesecond mobile device, monitor a channel of a land mobile radio systemassociated with the first mobile device, and maintain the database withthe first identifier associating the first mobile device with the landmobile radio system and the second identifier associating the secondmobile device with the cellular communications system; and to transitionfrom the first standby state to the second standby state upon failing toreceive the heartbeat signal from the first mobile device.
 2. The systemof claim 1 further comprising the controller configured in a firstcommunication state to coordinate receipt, at a first VoIP switch, of afirst communication from the first mobile device, and coordinatetransmission, at the first VoIP switch, of the first communication tothe second mobile device; and transition from the first standby state tothe first communication state upon receipt, in the first standby state,of a push-to-talk initiation signal from the first mobile device.
 3. Thesystem of claim 2 further comprising the controller configured in asecond communication state to coordinate receipt, at an RoIP gateway, ofa second communication from the first mobile device via the channel ofthe land mobile radio system associated with the first mobile device,and coordinate transmission, at the first VoIP switch, of the secondcommunication to the second mobile device; and transition from thesecond standby state to the second communication state upon receipt, inthe second standby state, of a push-to-talk land mobile radio signalfrom the first mobile device.
 4. The system of claim 3 furthercomprising the controller configured to transition from the firstcommunication state to the second communication state upon a degradationof the first communication from the first mobile device.
 5. The systemof claim 3 wherein the RoIP gateway converts the second communicationfrom a LMR protocol to a VoIP protocol, and the RoIP gateway includes afirst rack with a first module and a second module; the first mobiledevice and the second mobile device are in a first talk group associatedwith the first module; and a third mobile device and the fourth mobiledevice are in a second talk group associated with the second module. 6.The system of claim 5 wherein the controller is configured in the firstcommunication state to coordinate transmission, at the first VoIPswitch, the first communication to a first plurality of mobile devicesof the first talk group; and coordinate transmission, at the RoIPgateway, the first communication to a second plurality of mobile devicesof the first talk group.
 7. The system of claim 6 wherein the database,in the first communication state, associates each of the first pluralityof mobile devices with the cellular communications system and each ofthe second plurality of mobile devices with the land mobile radiosystem.
 8. The system of claim 5 further comprising: a console clientspecifically configured for reassigning the first mobile device from thefirst talk group to the second talk group.
 9. The system of claim 8wherein the first talk group is a police talk group, and the second talkgroup is a fire talk group.
 10. The system of claim 2 wherein the firststatus control signal includes an identifier of the channel of the landmobile radio system associated with the first mobile device.
 11. Thesystem of claim 2 wherein the transition from the first standby state tothe first communication state includes a Session Initiation Protocolinitiating a Real-time Transport Protocol between the first mobiledevice and the second mobile device.
 12. The system of claim 1 whereinthe first mobile device includes a land mobile radio connected to bothan intelligent vehicle network and a cellular communication device via aUniversal Mobile Access Radio Link Control module.
 13. A method ofproviding hardened mobile VOIP and LMR services, the method comprising:in a first state transmitting a status signal via a cellular datachannel to a first mobile device, receiving a heartbeat signal via thecellular data channel from the first mobile device, monitoring a firstland mobile radio channel for a first communication from a second mobiledevice, and associating, in a database, an identifier of the firstmobile device with cellular data communications; transitioning from thefirst state to a second state upon a failure to receive the heartbeatsignal; in the second state monitoring the first land mobile radiochannel for a first communication from the first mobile device andsecond mobile device, and associating, in the database, the identifierof the first mobile device with land mobile radio communications;transitioning from the first state to a third state upon receipt of apush-to-talk signal via the cellular data channel from the first mobiledevice; in the third state receiving, via the cellular data channel, acommunication from the first mobile device, converting the communicationfrom a VoIP format to LMR format, and transmitting the communication toa second mobile device via a land mobile radio format.
 14. The method ofclaim 13 further comprising transitioning from the second state to thefirst state in response to receipt of a heartbeat signal from the firstmobile device.
 15. The method of claim 13 wherein transitioning from thefirst state to the third state further includes establishing a hostedconference bridge between the first mobile device and the second mobiledevice.
 16. The method of claim 13 further comprising receiving aconfiguration signal from a dispatcher client; and in response toreceipt of the configuration signal disassociating the first mobiledevice from a first talk group and associating the first mobile devicewith a second talk group.
 17. The method of claim 13 further comprisingtransitioning from the first state to a fourth state upon detection of apush-to-talk signal on the first land mobile radio channel; in thefourth state receiving, via the first land mobile radio channel, acommunication from the second mobile device, converting thecommunication from an LMR format to a VoIP format, and transmitting thecommunication to first mobile device via the cellular data channel. 18.The method of claim 13 further comprising transitioning from the firststate to a fifth state upon receipt of a shut-down notice from the firstmobile device; and in the fifth state associating, in the database, theidentifier of the first mobile device with inactive communications. 19.The method of claim 18 further comprising in the fifth state providingan active device list to a dispatcher client, the active device listindicating the first mobile device is inactive.
 20. The method of claim13, wherein in the first state transmitting the status signal via thecellular data channel to the first mobile device includes transmittingthe status signal from a first VoIP controller, and receiving theheartbeat signal via the cellular data channel from the first mobiledevice includes receiving the heartbeat signal at a second VoIPcontroller located at least 10 miles away from the first VoIPcontroller.